Temporal and spatial dynamics underlying capacitative calcium entry in human colonic smooth muscle

Platelet-derived microvesicles induce calcium oscillations and promote VSMC migration via TRPV4

Rationale: Abnormal migration of vascular smooth muscle cells (VSMCs) from the media to the interior is a critical process during the intimal restenosis caused by vascular injury. Here, we determined the role of platelet-derived microvesicles (PMVs) released by activated platelets in VSMC migration. Methods: A percutaneous transluminal angioplasty balloon dilatation catheter was used to establish vascular intimal injury. Collagen I was used to activate PMVs, mimicking collagen exposure during intimal injury. To determine the effects of PMVs on VSMC migration in vitro, scratch wound healing assays were performed. Fluorescence resonance energy transfer was used to detect variations of calcium dynamics in VSMCs. Results: Morphological results showed that neointimal hyperplasia was markedly increased after balloon injury of the carotid artery in rats, and the main component was VSMCs. PMVs significantly promoted single cell migration and wound closure in vitro. Fluorescence resonance energy transfer revealed that PMVs induced temporal and dynamic calcium oscillations in the cytoplasms of VSMCs. The influx of extracellular calcium, but not calcium from intracellular stores, was involved in the process described above. The channel antagonist GSK219 and specific siRNA revealed that a membrane calcium channel, transient receptor potential vanilloid 4 (TRPV4), participated in the calcium oscillations and VSMC migration induced by PMVs. Conclusions: TRPV4 participated in the calcium oscillations and VSMC migration induced by PMVs. PMVs and the related molecules might be novel therapeutic targets for vascular remodeling during vascular injury.

Modelling Human Colonic Smooth Muscle Cell Electrophysiology

The colon is a digestive organ that is subject to a wide range of motility disorders. However, our understanding of the etiology of these disorders is far from complete. In this study, a quantitative single cell model has been developed to describe the electrical behaviour of a human colonic smooth muscle cell (hCSMC). This model includes the pertinent ionic channels and intracellular calcium homoeostasis. These components are believed to contribute significantly to the electrical response of the hCSMC during a slow wave. The major ion channels were constructed based on published data recorded from isolated human colonic myocytes. The whole cell model is able to reproduce experimentally recorded slow waves from human colonic muscles. This represents the first biophysically-detailed model of a hCSMC and provides a means to better understand colonic disorders.

Subcellular elevation of cytosolic free calcium is required for osteoclast migration

Osteoclasts are multinucleated cells responsible for the resorption of bone and other mineralized tissues during development, physiological remodeling, and pathological bone loss. Osteoclasts have the ability to resorb substrate while concurrently migrating. However, the subcellular processes underlying migration are not well understood. It has been proposed that, in other cell types, cytosolic free Ca(2+) concentration ([Ca(2+) ]i ) regulates cell protrusion as well as retraction. Integration of these distinct events would require precise spatiotemporal patterning of subcellular Ca(2+) . The large size of osteoclasts offers a unique opportunity to monitor patterns of Ca(2+) during cell migration. We used ratiometric imaging to map [Ca(2+) ]i within rat and mouse osteoclasts. Migration was characterized by lamellipodial outgrowth at the leading edge, along with intermittent retraction of the uropod. Migrating osteoclasts displayed elevation of [Ca(2+) ]i in the uropod, that began prior to retraction. Dissipation of this [Ca(2+) ]i gradient by loading osteoclasts with the Ca(2+) chelator BAPTA abolished uropod retraction, on both glass and mineralized substrates. In contrast, elevation of [Ca(2+) ]i using ionomycin initiated prompt uropod retraction. To investigate downstream effectors, we treated cells with calpain inhibitor-1, which impaired uropod retraction. In contrast, lamellipodial outgrowth at the leading edge of osteoclasts was unaffected by any of these interventions, indicating that the signals regulating outgrowth are distinct from those triggering retraction. The large size of mature, multinucleated osteoclasts allowed us to discern a novel spatiotemporal pattern of Ca(2+) involved in cell migration. Whereas localized elevation of Ca(2+) is necessary for uropod retraction, lamellipod outgrowth is independent of Ca(2+) -a heretofore unrecognized degree of specificity underlying the regulation of osteoclast migration.

A pathophysiology-based approach to the management of early priapism

Priapism is a rare condition that involves persistent penile erection for greater than 4 h. Distinct variants exist, each with unique characteristics. Ischemic priapism is a painful medical emergency that may occur as a result of veno-occlusion leading to hypoxia and tissue death. Recurrent bouts of ischemic priapism, or stuttering priapism, require treatment for individual attacks as well as long-term prevention. Non-ischemic priapism is associated with trauma and may be managed conservatively. Recent advances into the pathophysiology of priapism have allowed the development of treatment algorithms that specifically target the mechanisms involved. In this review, we outline the basics of smooth muscle contraction and describe how derangement of these pathways results in priapism. A pathophysiological approach to the treatment of priapism is proposed with duration-based algorithms presented to assist in management.

Evidence for altered circular smooth muscle cell function in lower esophageal sphincter of W/Wv mutant mice

Nitrergic neurotransmission to gut smooth muscle is impaired in W/W(v) mutant mice, which lack intramuscular interstitial cells of Cajal (ICC-IM). In addition, these mice have been reported to have smaller amplitude unitary potentials (UPs) and a more negative resting membrane potential (RMP) than control mice. These abnormalities have been attributed to absence of ICC-IM, but it remains possible that they are due to alterations at the level of the smooth muscle itself. Amphotericin-B-perforated patch-clamp recordings and Ca(2+) imaging (fura 2) were compared between freshly isolated single circular smooth muscle cells (CSM) from W/W(v) mutant and control mice lower esophageal sphincter (LES). There was no significant difference in seal resistance, capacitance, or input resistance in response to applied electrotonic current pulses between CSM cells from W/W(v) mutants and controls. Compared with control mice, RMP was more negative and UPs significantly smaller in CSM cells from mutant mice LES. Administration of caffeine induced an inward current in cells from both mutant and control mice, but the current density was significantly larger in cells from W/W(v) mutants. Membrane potential hyperpolarization induced by sodium nitroprusside was larger in cells from control mice vs. W/W(v) mutants. In addition, intracellular Ca(2+) transients induced by caffeine were significantly increased in cells from mutants. These findings indicate that LES CSM is abnormal in W/W(v) mutant mice. Thus some physiological functions attributed to ICC-IM based on experiments in smooth muscle of ICC deficient mice may need to be reconsidered.

Osteopontin signals through calcium and nuclear factor of activated T cells (NFAT) in osteoclasts: a novel RGD-dependent pathway promoting cell survival

Osteopontin (OPN), an integrin-binding extracellular matrix glycoprotein, enhances osteoclast activity; however, its mechanisms of action are elusive. The Ca(2+)-dependent transcription factor NFATc1 is essential for osteoclast differentiation. We assessed the effects of OPN on NFATc1, which translocates to nuclei upon activation. Osteoclasts from neonatal rabbits and rats were plated on coverslips, uncoated or coated with OPN or bovine albumin. OPN enhanced the proportion of osteoclasts exhibiting nuclear NFATc1. An RGD-containing, integrin-blocking peptide prevented the translocation of NFATc1 induced by OPN. Moreover, mutant OPN lacking RGD failed to induce translocation of NFATc1. Thus, activation of NFATc1 is dependent on integrin binding through RGD. Using fluorescence imaging, OPN was found to increase the proportion of osteoclasts exhibiting transient elevations in cytosolic Ca(2+) (oscillations). OPN also enhanced osteoclast survival. The intracellular Ca(2+) chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) suppressed Ca(2+) oscillations and inhibited increases in NFATc1 translocation and survival induced by OPN. Furthermore, a specific, cell-permeable peptide inhibitor of NFAT activation blocked the effects of OPN on NFATc1 translocation and osteoclast survival. This is the first demonstration that OPN activates NFATc1 and enhances osteoclast survival through a Ca(2+)-NFAT-dependent pathway. Increased NFATc1 activity and enhanced osteoclast survival may account for the stimulatory effects of OPN on osteoclast function in vivo.

Essential role for calcium waves in migration of human vascular smooth muscle cells

Vascular smooth muscle cell (SMC) migration is characterized by extension of the lamellipodia at the leading edge, lamellipodial attachment to substrate, and release of the rear (uropod) of the cell, all of which enable forward movement. However, little is known regarding the role of intracellular cytosolic Ca(2+) concentration ([Ca(2+)](i)) in coordinating these distinct activities of migrating SMCs. The objective of our study was to determine whether regional changes of Ca(2+) orchestrate the migratory cycle in human vascular SMCs. We carried out Ca(2+) imaging using digital fluorescence microscopy of fura-2 loaded human smooth muscle cells. We found that motile SMCs exhibited Ca(2+) waves that characteristically swept from the rear of polarized cells toward the leading edge. Ca(2+) waves were less evident in nonpolarized, stationary cells, although acute stimulation of these SMCs with the agonists platelet-derived growth factor-BB or histamine could elicit transient rise of [Ca(2+)](i). To investigate a role for Ca(2+) waves in the migratory cycle, we loaded cells with the Ca(2+) chelator BAPTA, which abolished Ca(2+) waves and significantly reduced retraction, supporting a causal role for Ca(2+) in initiation of retraction. However, lamellipod motility was still evident in BAPTA-loaded cells. The incidence of Ca(2+) oscillations was reduced when Ca(2+) release from intracellular stores was disrupted with the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor thapsigargin or by treatment with the inositol 1,4,5-trisphosphate receptor blocker 2-aminoethoxy-diphenyl borate or xestospongin C, implicating Ca(2+) stores in generation of waves. We conclude that Ca(2+) waves are essential for migration of human vascular SMCs and can encode cell polarity.

Sarcoplasmic reticulum function in smooth muscle

The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a "one model fits all" approach to this subject, we have tried to synthesize conclusions wherever possible.

Heterogeneity of muscarinic receptor-mediated Ca2+ responses in cultured urothelial cells from rat

Muscarinic receptors (mAChRs) have been identified in the urothelium, a tissue that may be involved in bladder sensory mechanisms. This study investigates the expression and function of mAChRs using cultured urothelial cells from the rat. RT-PCR established the expression of all five mAChR subtypes. Muscarinic agonists acetylcholine (ACh; 10 microM), muscarine (Musc; 20 microM), and oxotremorine methiodide (OxoM; 0.001-20 microM) elicited transient repeatable increases in the intracellular calcium concentration ([Ca(2+)](i)) in approximately 50% of cells. These effects were blocked by the mAChR antagonist atropine methyl nitrate (10 microM). The sources of [Ca(2+)](i) changes included influx from external milieu in 63% of cells and influx from external milieu plus release from internal stores in 27% of cells. The use of specific agonists and antagonists (10 microM M(1) agonist McN-A-343; 10 microM M(2), M(3) antagonists AF-DX 116, 4-DAMP) revealed that M(1), M(2), M(3) subtypes were involved in [Ca(2+)](i) changes. The PLC inhibitor U-73122 (10 microM) abolished OxoM-elicited Ca(2+) responses in the presence of the M(2) antagonist AF-DX 116, suggesting that M(1), M(3), or M(5) mediates [Ca(2+)](i) increases via PLC pathway. ACh (0.1 microM), Musc (10 microM), oxotremorine sesquifumarate (20 microM), and McN-A-343 (1 muM) acting on M(1), M(2), and M(3) mAChR subtypes stimulated ATP release from cultured urothelial cells. In summary, cultured urothelial cells express functional M(1), M(2), and M(3) mAChR subtypes whose activation results in ATP release, possibly through mechanisms involving [Ca(2+)](i) changes.